1. Technical Field
The present invention relates to a test apparatus and a circuit module.
2. Related Art
Semiconductor devices included in electronic circuits generate heat when they operate. The amount of heat generated by semiconductor devices are increasing as operation speeds of the semiconductor devices have been increasing and circuits are more densely integrated with the recent years' development. Accordingly, it is essential to cool a plurality of semiconductor devices mounted on a test substrate. In a semiconductor test apparatus, for example, a multi-layered test substrate on which electronic circuit elements such as semiconductor devices are mounted is covered with a fluid casing, and coolant is circulated within the fluid casing to cool the semiconductor devices on the test substrate (see Patent Document 1). Here, Patent Document 1 is Japanese Patent Application Publication 2002-280507.
FIG. 14 illustrates a conventional method to cool a test substrate on which electronic circuit elements such as semiconductor devices are mounted. Referring to FIG. 14, a multi-layered test substrate 100 is formed of insulating plates 102, 103 that are made of epoxy resin or the like and bonded to each other with prepreg 104 such as a glass fiber substrate. Electronic circuit elements including a semiconductor device 106 are provided on the both sides of the test substrate 100. The test substrate 100 is coupled to another test substrate via a connector 108. In order to mitigate temperature elevation due to the heat generated by the semiconductor devices 106, a fluid casing 110 is provided to attach to the test substrate 100, and the semiconductor device 106 is cooled with coolant such as fluorine-based liquid which is filled within an enclosed space 112 between the test substrate 100 and the fluid casing 110.
FIG. 15 is an enlarged view of a portion including the connector 108 shown in FIG. 14. Referring to FIG. 15, the semiconductor device 106 is coupled to a terminal 114 of the connector 108 via a first wiring line 116 that is formed of a copper foil or the like and provided on a surface of the insulating plate 102, a penetrating through-hole 120, a second wiring line 118 that is provided within the layer of the insulating plate 102, a penetrating through-hole 121, a third wiring line 117 that is provided on the surface layer of the insulating plate 102, and a connection terminal 122. In the same manner, a wiring line 119 is provided inside the layer of the insulating plate 103. When the wiring line 118 and the wiring line 119 are disposed closely to each other, cross-talk occurs between the wiring line 118 and the wiring line 119. In order to secure a certain distance between the wiring line 118 and the wiring line 119, the wiring line 118 and the wiring line 119 are formed inside the insulating plate 102 and the insulating plate 103 respectively rather than the interfaces between the prepreg 104 and the insulating plates 102 and 103.
However, when the wiring line 118 is formed inside the insulating plate 102, a stub can be formed between an intersection of the penetrating through-hole 120 and the wiring line 118 and an intersection of the penetrating through-hole 120 and the prepreg 104. Stub formation creates a problem that signal waveforms are deformed due to the effect of reflection at edges of the penetrating through-hole 120.
In addition, there will be another problem such that high-frequency components of the deformed signals are emitted to the outside of the test substrate 100 as noise. Particularly when the frequency of the transmitted signal exceeds 2 GHz, the adverse effects of the above-stated problems caused by the stub becomes pronounced. By using a surface via hole (SVH) and an inner via hole (IVH), it is possible to avoid cross-talk and a stub from being generated. However, providing SVHs and IVHs is an expensive process so that the manufacturing cost of the test substrate will be increased.